With development of wireless communications technologies, wireless devices such as a base station, a wireless intelligent device, and a wireless terminal that are in a wireless communications system need to support multi-user concurrent processing. The wireless devices may include but are not limited to, a smartphone with multiple subscriber identification module (SIM) cards, a Bluetooth® device supporting a multipoint connection, a Wireless Fidelity (WiFi) device, a radio base station, and the like.
Generally, channels in the wireless communications system are classified as a control channel used to transmit control information and a data channel used to transmit service data. The control information transmitted on the control channel generally includes a pilot and a control parameter. In an embodiment, the pilot is known to a receiver in a communication. The receiver compares a received pilot with a known pilot, to obtain a channel model of a wireless channel which is located between the receiver and a transmitter, and the receiver further performs a “channel estimation” using the channel model. Thereafter, the receiver decodes, according to a channel estimation result, service data received over the data channel to complete the communication on the data channel.
During multi-user concurrency, a modulation of different users is performed on a carrier according to a manner such as code division, time division, or frequency division. Due to reliability issues of a wireless device such as a multipath effect of space transmission by way of example, interference exists between channels of different users. Therefore, a deviation exists in the channel model obtained by the receiver during channel estimation, which causes distortion of service data received over the data channel by the receiver. A parallel interference cancellation technology may be used to cancel the interference between the channels of the different users.
A basic principle of parallel interference cancellation is as follows:
A wireless device receives a real-time signal C, where C includes modulation data of two users A and B; then the wireless device calculates a transmission model of A, and then restores a received signal A′ of A according to the transmission model of A obtained by means of calculation; the wireless device subtracts A′ from the real-time signal C to obtain a remained data of the user B; and finally, a transmission model of B is calculated based on the remained data of the user B.
In a process in which the wireless device subtracts A′ from the real-time signal C, noise of the user A may be removed to reduce multi-user interference to the user B, where the processing is generally referred to as “antenna data cancellation”. The received signal A′ of A is restored according to the transmission model of A obtained by means of calculation, which is generally referred to as “antenna signal regeneration”.
FIG. 1 shows a parallel interference cancellation scheme. For simple illustration, only two concurrent users are shown as a user A and a user B.
In the parallel interference cancellation scheme shown in FIG. 1, a radio signal that includes antenna data of a control channel of the user A, antenna data of a data channel of the user A, antenna data of a control channel of the user B, and antenna data of a data channel of the user B is collected by “collecting data by using an antenna”. The radio signal is processed by a “control channel descrambling and despreading apparatus” to obtain baseband data of the control channel of the user A and baseband data of the control channel of the user B. Next, a “control channel model estimation apparatus” performs a channel estimation on the baseband data of the control channel of the user A and the baseband data of the control channel of the user B to obtain channel estimation results of the user A and the user B. A “control channel data regeneration apparatus” performs processing, such as spreading and scrambling opposite to the “control channel descrambling and despreading apparatus”, on the obtained channel estimation results to respectively obtain regenerated antenna data of the control channel of the user A and regenerated antenna data of the control channel of the user B. Because the regenerated antenna data is corrected by a channel model, such as the “control channel model estimation apparatus”, reliability of the regenerated antenna data is higher than that of original antenna data.
A “data channel interference canceller” subtracts the regenerated antenna data of the control channel from received antenna data to obtain the antenna data of the data channel of the user A and the antenna data of the data channel of the user B. The subtraction performed by the “data channel interference canceller” further cancels interference between control channels of the two users and achieves parallel interference cancellation. A “data channel descrambling and despreading demodulator” processing and a “decoding and post processing” are separately performed on antenna data output by the “data channel interference canceller” to obtain baseband data of the data channels of the two users.
Generally, the “control channel model estimation apparatus” includes a filtering process. In order to acquire a correct channel estimation result, a long filtering window is needed to collect window data for an extended period of time.
Due to an extended period of time required to obtain the channel estimation result and parallel interference cancellation cannot be started in the beginning, early interference cannot be well canceled. Consequently, as a cause-effect system, amplified interference noise occurs later in the wireless communications system that follows the law of causation.